Myopia is emerging as a major public health issue due to its increasing prevalence and long-term pathological outcomes. Prevention must focus on limiting excessive axial elongation which is the cause of both myopic refractive error and its pathological outcomes. The increasing prevalence appears to be due to environmental changes involving near work, rather than to a genetic failure of emmetropisation. Attempts to control the progression of myopia optically have been unsuccessful; the only available preventive regime involves the use of atropine eye drops. This regime has short-term side effects, and since the site and mechanism of action of muscarinic antagonists are unclear, there are concerns about its long-term safety. Recent studies on natural STOP growth signals suggest that they are evoked by relatively brief periods of imposed myopic defocus, and can overcome strong pressures towards increased axial elongation. While STOP signals have only been successfully used in chickens to prevent excessive axial elongation, similar signals are generated in mammals and non-human primates. Further studies may define the conditions under which this approach could be used to prevent the development of myopia in humans.
Myopia in humans results from an imbalance between the refractive power of the cornea and lens and the axial length of the eye, such that the image of an object at infinity falls in front of the retina, with the lens at rest. Accommodation, therefore, cannot focus the blurred images of distant objects.
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